What's your favorite shock cord knot?

I've used a buntline hitch and a uni/Duncan knot for attaching shock cords to nose cones and on the first couple rockets I built, I just made some random knots I had to cut off later. I forget how I found the buntline hitch, but I think I found the uni knot on the Model Rocket Building blog.

Do you have a preferred type knot for shock cords? Do you like something that can be removed if need be?

I use a bowline for all my shock cord knots.

timbucktoo said:

I use a bowline for all my shock cord knots.

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You know what's weird? I used a bowline for tying the nose cone onto my friend's Apogee Aspire. We thought the rocket was lost, but after driving around, I found it a half mile later - but the nose cone was gone. I have no idea how this happened! The bowline was the only knot I knew how to tie for years, but I really did know how to tie it.

So was the knot untied or did the the line just part? I've never had any issues and I read it somewhere that that's the knot of choice for shock cords.

For attaching parachutes to the middle of the line, I use an alpine butterfly knot, and a figure eight follow through on the ends to connect to the eye bolts.

for the ends of the cord I've been using a simple overhand loop. hasn't failed me yet but I'm looking for a better knot that doesn't take up too much space. for a loop in the middle I'm using the alpine butterfly. and right on the animatedknots.com site it says the bowline will untie if unloaded...

I'm a buntline guy too. I've also done a tautline and have never had problems with either.


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Bowline on a bight for me if it's at the end of a line.

I have found that I use/need 3 different knots for rocketry:
1. Stevedore knot -- a stopper knot used at the terminal ends of cords, i.e., for shock cord to nose cone or kevlar to eye-bolt.
2. Slim Beauty -- connects two lines to each other, specifically, knotting kevlar cord to an elastic cord
3. Alpine Butterfly knot -- to connect parachute to shock cord.

All of these are demonstrated beautifully at animatedknots.com

Years ago I used to use a bowline for attaching Nosecones to shockcords but I switched ages ago to 3 half hitches when tying both Kevlar or Elastic to NC loops or screw eyes. Have also used the Improved Clinch knot for tying Swivels to chutes and Streamer attachment lines.

Chute or streamer attachements are always mid-shockline with a butterfly knot.

Anchor knots around motor mounts or Thrust rings is either 3-half hitches or a bowline depending on the diameter of the line being tied.

In more the 45year have never lost a nosecone to a knot failure. have snapped a few short shockcords along the way

I sew loops into the shock cords by hand with needle and thread, then cover the job with heat shrink tubing for a clean look.
I sometimes use knots as a temporary thing when I just want to fly a new rocket to try it out, but I get them sewn properly asap.

timbucktoo said:

So was the knot untied or did the the line just part? I've never had any issues and I read it somewhere that that's the knot of choice for shock cords.

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Well, I'm not sure. The knot was missing, that's for certain. I assumed it had come untied, because Kevlar is so strong, and there was no zipper or any other damage (other than a fin snapped off on landing and a shredded streamer, which was just taped on, but still there). But I can't be sure.

Micromeister said:

Years ago I used to use a bowline for attaching Nosecones to shockcords but I switched ages ago to 3 half hitches when tying both Kevlar or Elastic to NC loops or screw eyes. Have also used the Improved Clinch knot for tying Swivels to chutes and Streamer attachment lines.

Chute or streamer attachements are always mid-shockline with a butterfly knot.

Anchor knots around motor mounts or Thrust rings is either 3-half hitches or a bowline depending on the diameter of the line being tied.

In more the 45year have never lost a nosecone to a knot failure. have snapped a few short shockcords along the way

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So, if you use swivels for chutes and streamers, do you attach a swivel mid-line and then attach a chute when you're ready to fly, or do you just tie a loop and hook the swivel on later?

I'm going to have to check out this Alpine Butterfly Knot - I've never heard of it, but sounds like it's popular for certain uses.

The alpine butterfly it's a secure knot for creating a loop mid line while maintaining almost the full line strength.

o1d_dude said:

Bowline on a bight for me if it's at the end of a line.

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+1 Bowline on a bight...use it all the time and have never had it fail

Here is a really good source for knots https://www.netknots.com/rope_knots/bowline-on-a-bight/

lcorinth said:

So, if you use swivels for chutes and streamers, do you attach a swivel mid-line and then attach a chute when you're ready to fly, or do you just tie a loop and hook the swivel on later?

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always add a snap swivel to ALL Chutes and Streamers (unless competition type) so recovery device can be field adjusted to suit the current weather conditions. On the field the swivel is attached to the shock-cord in-line Butterfly knot.

The butterfly is a super easy knot to tie. see below.

Since I always use elastic shock cords on low power rockets, I have never had a fail with a simple overhand knot done twice to the nose cone. On some of my bigger LPR and scratch MPR, I still use elastic, but I'll take a 1/2" wide key ring and put a larks head knot on it, 1/3 the of the way from the nose cone on the shock cord. I've never had a problem with either of those knots. If I remember to do it, I'll hit em with a few drops of CA as insurance. My rockets don't get a lot of flight time though.

I use double surgeons on everything.

Uni-knot.

Micromeister said:

always add a snap swivel to ALL Chutes and Streamers (unless competition type) so recovery device can be field adjusted to suit the current weather conditions.

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I do too, since I read of the idea, but I always attach it to the nose cone. Never occurred to me to attach it mid-line.

Micromeister said:

always add a snap swivel to ALL Chutes and Streamers (unless competition type) so recovery device can be field adjusted to suit the current weather conditions. On the field the swivel is attached to the shock-cord in-line Butterfly knot.

The butterfly is a super easy knot to tie. see below.

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That's totally using way too much material. Total "Overknotting".

People like you using knots are the BANE of shock cord attachment.
A much lighter join can be had by simply sewing it the RIGHT way.:wink:

Uni-knot. First knot I ever learned when I was a kid (from the instructions in a spool of Stren fishing line). I use it for everything, but it can be hard to un-tie if needed. For those cases, I use a bowline.

I also use bowlines. The animated knots site makes it easy to learn how to tie knots.

I haven't been doing this for as long as others, but as of right now I use figure-8 for attaching things to the end of lines where it's high-stress, bowline for places that aren't as high stress or I don't care as much, and Alpine Butterfly for things like attaching the NC to the middle of the shock cord. Alpine Butterfly is one of very few knots that handle triaxial loading well and has a stable loop, and is thus the only knot I trust for that.

I use boline or bowline, however you want to spell it.

What many don't realize about this knot is that it has a failure mode. There are two main versions (at least), one where the tail end is on the inside of the loop, and one with the tail end on the outside. The failure mode for both is something pushing the tail end back into the knot, loosening it.

This is readily prevented by a couple wraps of masking tape securing the end to the loop. Now it won't come apart without being ripped apart.

I've also seen rocket people fail to tighten this knot correctly, making it much easier for it to come undone.

Gerald

I'm surprised no one has mentioned a buried end splice for tubular materials. Everything I do has buried end loops at each end and a butterfly in the middle if needed.

A taut line hitch so I can unattach the shock cord without a quick link.

Then a knot that I don't remember the name for for attaching the chute.

I use a water knot in webbing to make a loop that I then attach to a quick link. A water knot is just an overhand knot traced back over itself.

Joe

Water knot if I'm using some type of webbing. Great for each end. Supposedly keeps 64% of original breaking strength. Love the alpine butterfly for any type of mid-line attachment. Buried eye splices are to tricked out for me but I would imagine if properly done, conserve the web's strength the most.
_ken